Baking soda for kidney patients

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Behind the Headlines

Friday July 17 2009

Dialysis removes waste products and unwanted water from the blood

“A daily dose of baking soda could help patients with chronic kidney disease avoid having to undergo dialysis,” reported The Times. It said that research has found that sodium bicarbonate can dramatically slow the progress of the condition. The newspaper said that patients given a small daily dose of sodium bicarbonate over a year, had only two-thirds of the decline in kidney function experienced by people given usual care.

This randomised controlled trial found that people with both chronic kidney disease and metabolic acidosis (low blood bicarbonate/high blood acidity) benefited from oral bicarbonate supplements over a two-year period. The study has some shortcomings, but provides strong evidence that these supplements could be used in treatment. The researchers have called for further research to confirm their findings.

The exact place of this in standard treatment for people with chronic kidney disease is not yet known. In practice, people with severe renal disease may receive sodium bicarbonate as part of their treatment in hospital anyway.

Where did the story come from?

The research was carried out by Dr Ione de Brito-Ashurst and colleagues from the Department of Renal Medicine and Transplantation, at the William Harvey Research Institute Barts, and the London NHS Trust in London. The study was published in the Journal of the American Society of Nephrology.

What kind of scientific study was this?

This randomised controlled trial investigated the effects of bicarbonate supplementation for people with chronic kidney disease and metabolic acidosis.

Metabolic acidosis is a condition where there is an acid-alkali imbalance in the blood, that results in high blood acidity (low pH) and low plasma bicarbonate levels. Several conditions can lead to metabolic acidosis, including heart failure, drugs or toxins, kidney failure or diabetic ketoacidosis (caused by high blood sugar resulting from reduced insulin). It is a common complication in people with advanced chronic kidney disease, and it can interfere with protein metabolism and may lead to stunted growth (in children) and loss of bone and muscle.

The study looked at 134 patients with chronic kidney disease and low blood bicarbonate levels (i.e. with metabolic acidosis). The patients were randomly allocated to either sodium bicarbonate supplements, 600mg taken orally three times a day (increased as necessary to achieve and maintain blood levels), or to usual care for two years.

The researchers excluded from the study anyone with morbid obesity, cognitive impairment, chronic sepsis, congestive heart failure or uncontrolled blood pressure. Over the course of the two-year treatment, they assessed the rate at which creatinine was cleared by the kidneys (creatinine clearance). Creatinine is a waste product that healthy kidneys can remove. Measuring how successfully they do this is a marker for the severity of kidney disease. The researchers had a theory that bicarbonate supplementation would reduce the rate of decline of creatinine clearance in people with chronic kidney disease, and that it would reduce the number of patients whose kidney disease rapidly progressed towards established renal failure. To measure this, the participants provided 24-hour urine samples (collecting every drop of urine during each period) every two months.

The researchers defined rapid progression as a reduction of creatinine clearance of more than three ml/min per 1.73m2 per year.

What were the results of the study?

People given sodium bicarbonate supplements had significantly higher blood bicarbonate levels than those given standard care. Blood pressure control was similar between the groups even though those receiving supplements were also taking in more sodium (which could increase blood pressure).

Age and gender also affected the rate of decline of creatinine clearance, but when these were taken into account, supplementation still had a significant effect. Adverse events were similar in both groups. Supplementation was also associated with better nutritional status, including improved protein intake and more normal protein metabolism.

What interpretations did the researchers draw from these results?The researchers conclude that supplementation with oral bicarbonate in patients with chronic kidney disease and low plasma bicarbonate (metabolic acidosis) slows the rate of decline in kidney function and lowers the chances of developing end-stage renal disease. OK? They say that this cheap, simple strategy also improves the nutritional status of patients and has the potential to translate into significant economic and quality of life gains, as well as clinical benefits.

What does the NHS Knowledge Service make of this study?

This randomised controlled trial provides good evidence that oral supplementation with bicarbonate can improve clinical outcomes for people with chronic kidney disease and associated metabolic acidosis. The researchers discuss the strengths and weaknesses of their study:

The randomised nature of the study, the intention to treat analysis (i.e. including all participants in analysis even those who dropped out) and study size are all strengths that increase confidence in this trial’s findings.

The results are likely to be applicable to many patients with chronic kidney disease because the study sample was heterogeneous – i.e. the patients had a wide range of underlying conditions.

However, the findings won’t necessarily apply to those with morbid obesity, cognitive impairment, chronic sepsis, congestive heart failure or uncontrolled blood pressure, as these groups were excluded from the study.

The study did not have a placebo group, and instead compared supplementation with standard care. It is not clear what was involved in standard care, nor whether taking other drugs that may interfere with sodium bicarbonate, such as the phosphate binders, differed between the groups.

Patients receiving the supplements would have known that they were in the intervention group, i.e. they or the researchers were not blinded to the group allocation. This could have introduced some bias.

The researchers themselves call for validation of their study through a double-blind, placebo-controlled, multicentre trial that will provide stronger evidence of the effects of oral bicarbonate supplementation for people with chronic kidney disease.

The exact place of this in standard treatment for people with chronic kidney disease is not yet known. In practice, people with severe renal disease may receive sodium bicarbonate as part of their treatment in hospital anyway.